Unlocker
- Unlocks files/folders that are in use.

CCleaner
- Scan/fix registry issues, cleans out temporary files.
Make sure to download the “Slim” build, it doesn’t contain any unneeded extras.

PageDefrag
- Defrags your PageFile, Hibernation File, and system registry files. (Doesn’t work with Vista!)

AutoRuns - Lets you view and change items that load on your computer or run on startup.

Mozilla Firefox
- Simply the best web browser, ever.

Firefox must-haves:

Qute Theme
- One of the better themes for Firefox. The default for version 0.8.

Adblock
- Blocks images, banners, iFrames, and other stuff you may not want to see. (I prefer this over “Adblock Plus” for many reasons.)

NoScript
- Blocks all JavaScript unless you decide to allow it. Stops many annoying web issues.

IE Tab (Windows Only)
- Changes the rendering engine of the current tab to Internet Explorer. Allows you to use sites like Windows Update through Firefox.

FlashGot
- Lets Firefox work with many popular download managers.

Nice Firefox Extras:

Colorful Tabs
- Makes each tab a different color.

StumbleUpon
- Jump around to random pages that have to do with what you like.

VideoDownloader
- Lets you save videos that you find on YouTube and Google Video.

Del.icio.us
- Adds a button to tag the current page to add to your Del.icio.us bookmarks.